122 Chapter 7 first 2 years of life, in the context of posterior fossa maldevelopment.35 It may be that the association between lambdoid craniosynostosis and cortical thinning is related to increased ICH rates, which then differentially affects more susceptible cortical regions such as the cingulate gyri. The explanation for why ICH rates may be elevated in lambdoid synostosis is crowding of the posterior fossa leading to venous outflow obstruction and/or accessory venous drainage pathways, which are common in CP syndrome.36 Furthermore, contralateral growth restriction of the occiput may result in a cranial distortion mirrored by that of the pericallosal artery supplying the cingulate cortex; however, further study is needed to evaluate this possibility. Coronal suture involvement was also associated with cortical thinning across all brain regions measured; however, its effects were generally small (Cohen’s d < 0.5) except for frontal lobes. But even in frontal lobes, the effect was not definitive, as 95% confidence intervals included zero at their outer limits. Despite this, it seems that some localized influence does exist, and a more comprehensive explanation is required to resolve these apparent discrepancies. Due to the fact that lambdoid and coronal synostosis both result in significant skull distortion, including flattening of the occiput, scoliosis of the face and turribrachycephaly, dependent upon specific suture combinations, we must consider the influence of overall cranial shape and its contribution to ICH and subsequent cortical changes. It may be that turribrachycephaly contributes to frontal cortical thinning, which occurs in bicoronal and bilambdoid synostosis, while isolated lambdoid suture involvement contributes more heavily to ICH development, disproportionately impacting the cingulate gyri. The idea that cranial shape influences neurodevelopment is supported by previous study in non-syndromic craniosynostosis patients who experienced worse developmental and linguistic outcomes than healthy children or patients with varying forms of single suture synostosis.37-40 Our results similarly show cortical thickness effect sizes corresponding to these outcomes, with sagittal synostosis resulting in increased cortical thickness across various brain regions, most notably in the occipital lobes. When interpreting the results of our study, several limitations should be considered. First, 34 patients were included for analysis, which limits the power of our study to draw negative inferences and could explain our failure to discover any cortical changes associated with type of primary cranial vault expansion. Almost all scans were postoperative in this study. Ideally, cortical thickness data pre and postoperatively would be obtained from serial imaging studies; however, this was not possible due to the early age of surgery (median 1.27 years) and the lack of adequate tissue contrast inherent in infant brains on MRI.41 Additionally, it is possible that other variables unaccounted for in our analysis, which may influence cortical development, could have resulted in reverse confounding, thereby masking any effect of surgical intervention type. Finally, the precision of FreeSurfer processing methodologies may be influenced by cranial dysmorphology. FreeSurfer generates maps using spatial intensity gradients
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